(1) Field of the Invention
This invention relates to new and improved gyroscopes. More particularly, the invention relates to a method and apparatus for compensating two-axis gyroscopes for inertial drift.
(2) Description of the Prior Art
A gyroscope is, generally, a flywheel or other rotating body which can be rotated at a high angular velocity and which is mounted in two gimbal sets in order to take advantage of the tendency of the rotating body to remain in a fixed position relative to inertial space. By means of suitable measuring devices connected between the gimbals and between the outer gimbal and a vehicle carrying the gyroscope, the position of the gyroscope may conveniently be related to X and Y axes with respect to the vehicle itself. The measuring devices may be dials or angle transducers which transmit the angles measured to remote indicators.
If gyroscopes were perfect, that is, if there were no friction in the gimbal bearings and, if there were no extraneous sources of torque, such as imbalance, etc., the inertial rate that the flywheel would experience would be zero and true angular measurements would be obtained. Even though the vehicle were moving around the gyroscope, the inner flywheel would be totally undisturbed. In actuality, imperfections inherent to some degree in every gyro cause drift of the gyroscope to occur. This is caused by the application of a torque tending to change the direction of the spindle axis. Gyroscope users have learned to live with the drifts produced by such imperfections and to correct them either by hand, periodically, or by using very sophisticated terrestrial kinetic measurements and autobiasing techniques which involve measuring and comparing and slaving the device to the earth. In other words, the rate of drift is determined and compared to the known rate at a given latitude, and a correction is made.